1. Field of the Invention
The present invention relates to a capacitor device and to an electrical power conversion device.
2. Description of Related Art
For some years now, the market for hybrid automobiles (HEV: Hybrid Electric Vehicle) and for electric automobiles (EV: Electric Vehicle) has seen rapid spread and development, and as a result there have been greater and greater demands upon electrical equipment for HEVs, such as batteries, inverters, motors and so on, in terms of requirements for higher output, better compactness, and lower cost. In particular, there are great demands upon inverter devices to be used for HEVs and EVs for increase in voltage, higher density, and better compactness, in order to implement lower fuel consumption, reduction of electrical power consumption, and reduction of the space occupied.
Apart from incorporating a power module that contains power semiconductor elements such as IGBTs or the like and bus bars and so on, an inverter device is assembled from components such as capacitors (DC-link capacitors) for smoothing DC power and so on. In particular, as a capacitor for an inverter device for an HEV or an EV, since the voltage that is used is several hundreds of volts, in many cases a film capacitor having high withstand voltage is principally used. Apart from film capacitors being distinguished by having high withstand voltage, the fact that, unlike other types of capacitor, they have the strong points of low loss, a long maintenance free life, and the self-healing characteristic consisting of the capability to recover by themselves when their film insulation has broken down, may also be advanced as reasons why they are often employed in HEVs and EVs.
Generally, film capacitors are made by vapor depositing a metal such as aluminum or the like upon at least one surface of an organic dielectric film made from PET (polyethylene terephthalate), PP (polypropylene), or the like, thus producing a metallized film, winding up two superimposed layers of this metallized film, and manufacturing two metallikon electrodes by metallizing the end surfaces of the wound up capacitor element with a metal such as aluminum or zinc, in order to bring electrodes out to the exterior.
In a capacitor device for an inverter device for an HEV or an EV, for example, terminals for electrical connection to other components are connected to these metallikon electrodes at the two ends of the film capacitor element by welding or soldering or the like. In many cases, the film capacitor element is then housed in a resin case that is made from PPS (polyphenylene sulfide) resin, PBT (polybutylene terephthalate) resin, or the like, and the space between the resin case and the film capacitor element is sealed with an insulating and sealing resin (i.e. a potting resin) such as epoxy resin, urethane resin, or the like, whereby a sealed capacitor module is manufactured. The insulating and water-proof characteristics of this film capacitor element are ensured by the resin case and the potting resin.
A capacitor device in which a case made from resin is used is light in weight and is excellent in heat resistance, but, under conditions in which the output electrical current is large and high ripple currents flow in the capacitor, the generation of heat by the internal capacitor element becomes high, and, due to the resin material from which the case and the potting are manufactured, this heat accumulates in the interior of the capacitor device, so that there is a danger of deterioration of its electrical characteristics such as its breakdown voltage and so on. On the other hand, it is per se known to manufacture the case from an electrically conductive metallic material and to flow potting resin into the space between the capacitor element and the case, so that a good insulating characteristic and a good heat dissipation characteristic can both be obtained. In other words, it is per se known to manufacture a capacitor device by inserting the capacitor element into a case that is made from metal while orienting the metallikon electrodes on opposite sides of the capacitor element towards the opening at the top of the case and towards the bottom surface of the case, and by potting a resin material that has high thermal conductivity into the case between its bottom surface and the lower side of the lower metallikon electrode, while potting a resin material that has high mechanical strength into the other spaces between the case and the capacitor element. With this capacitor device, it is possible to dissipate heat generated by the capacitor element to the metallic case via the high thermal conductivity resin layer that is formed in the lower portion of the case (refer to Patent Document Japanese Laid-Open Patent Publication 2006-196680).